In the following description, reference is made purely by way of example to packing machines for producing rigid packets of cigarettes.
Units for supplying blanks on cigarette packing machines, such as the one described for example in U.S. Pat. No. 5,029,834, comprise a suction pickup head moved cyclically by a crank mechanism substantially back and forth between a pickup position, in which the head engages a bottom opening in a blank store to withdraw a blank, and an unloading position, in which the head feeds the blank onto a conveyor roller.
Though perfectly satisfactory, supply units of the type described above fail to meet the high operating speeds (over 600 packets a minute) demanded by modern cigarette packing machines, owing to the inertia and vibration produced by the substantially reciprocating movement of the pickup head.
FR-A-2,478,576 discloses a packing machine having a unit for supplying blanks and comprising a store for storing blanks, the store having a bottom opening, a pickup head for withdrawing a respective blank and located on a plate connected to a wheel rotating continuously about a first axis to feed the pickup head along an endless path extending through a loading station where the pickup head engages the bottom opening to withdraw a blank. The plate is connected to the wheel to oscillate, with respect to the wheel, about a second axis parallel to the first axis by means of an actuating device.
The supplying unit disclosed in the aforementioned FR-A-2,478,576 is capable to operate at a speed higher than that of the supplying unit disclosed in U.S. Pat. No. 5,029,834, but is not capable to operate with satisfactory results at the high operating speeds (over 600 packets a minute) demanded by modern cigarette packing machines owing to the fact that, at such speed, the pickup head, by moving in a substantially radial direction in relation to the wheel, is not given a sufficient time to properly engage the blank to be withdrawn.